In petroleum refining industry, the alkylation reaction between isobutane and butene (also referred as C4 alkylation or isobutane alkylation) is an important process for producing clean high-octane gasoline blending component. It has been known that the catalyst used in the alkylation reaction may comprise hydrofluoric acid, concentrated sulfuric acid and ionic liquids, wherein hydrofluoric acid and concentrated sulfuric acid are conventional industrial catalysts for this process. Both of hydrofluoric acid and concentrated sulfuric acid exhibit satisfactory properties in terms of activity, selectivity and catalyst lifetime, however, they may result in some problems such as environmental pollution, equipments corrosion as well as personnel injuries etc., thus, the industrial development of C4 alkylation being limited seriously.
As a novel compound system, ionic liquids have the properties such as being environmental friendly, less corrosive, low toxicity, adjustable acidity and physical-chemical properties, being easily separated from the product as well as being recycled at high rate, so that to become a novel desired catalytic material to be used for C4 alkylation instead of those liquid strong acids such as hydrofluoric acid and concentrated sulfuric acid. U.S. Pat. No. 7,285,698 and CN 1500764A respectively disclosed the catalytic processes for the alkylation reaction between isobutane and butene using a composite ionic liquid as catalyst, wherein the yield of the alkylation product—alkylate oil may be up to 170-180% by volume of the alkene feed, C8 fraction may constitute 60-80% of the alkylate oil, most prominently trimethylpentane may be more than 70% of C8 fraction, and RON (Research Octane Number) may be of 93-98.
More and more researches have been made on the ionic liquids regarding their properties and utilizations due to their multiple benefits as catalysts. However, the researchers have found that there are still some practical difficulties to be overcome when the ionic liquids being used as catalysts in the alkylation reaction. No matter the simple ionic liquid, of which the anion is derived from a single metallic compound, or the composite ionic liquid is used as the catalyst in the catalytic alkylation reaction, the catalyst will get deactivated inevitably. The feed amount processed by per gram of the ionic liquid catalyst can hardly be more than 100 g, thus, the ionic liquid catalyst had to be replaced and regenerated frequently and the corresponding industrial process would be limited apparently. There are also some researches providing technical solutions based on the believed reasons why the ionic liquid catalyst getting deactivated. For example, Chinese patent application 200710063459.6 disclosed a process for prolonging the catalyst life by using metallic aluminum or aluminum trichloride as aluminum source to compensate the aluminum trichloride lost due to entrainment in oil phase and hydrolysis of ionic liquid in the presence of water. The inventors of this application have found that the primary reason for chloroaluminate as ionic liquid catalyst getting deactivated is the loss of the active aluminum trichloride therein decreases the reaction activity, and the loss of aluminum trichloride is primarily due to the hydrolysis of aluminum trichloride caused by the inevitable water in the reaction feed and further possibly due to that aluminum trichloride may be entrained into oil phase due to complexation with some strong electron-donating species, which may be present in the reaction system. Thus, said patent application provided a process for producing alkylate oil, wherein the ionic liquid catalyst is regenerated on line continuously by using metallic aluminum or aluminum trichloride as aluminum source to compensate the aluminum trichloride lost due to entrainment in oil phase and hydrolysis of ionic liquid so as to makeup aluminum continuously and extend the catalyst life. Said patent application further stated that the process can also reduce the amount of HCl present in the catalytic reaction system, thus maintaining the selectivity of the targeted isooctane in the product at high level and reducing the corrosion due to the presence of HCl. However, a series of patent documents such as Chinese patent application CN 200680051282.1, CN 200680052353.X, United States Patents USP 20070142211 and USP 20070142214 disclosed processes for regenerating ionic liquid catalysts used in alkylation reaction by removing mixed polymers therefrom because it is believed that the ionic liquid catalysts get deactivated due to their anionic components being deactivated by the mixed polymers.
Therefore, it is very important to effectively overcome the deactivation of the ionic liquids in order to develop and promote their uses as commercial catalysts for producing alkylate oil.